1. Field of the Invention
The present invention relates to a magnetic sensor and a magnetic head. More particularly, the present invention relates to a magnetic sensor, of a CPP (current perpendicular to plane) type, for supplying a current in the direction perpendicular to the surface of a magnetic sensor layer. The magnetic sensor is used in a reproduction head, i.e., a read head, of a magnetic recording apparatus such as a hard disk drive (HDD). The magnetic sensor is characterized in that the resistivity (specific resistance) of a hard layer, of a hard magnetic material, acting as a magnetic domain control layer is controlled. The present invention also relates to a magnetic recording apparatus using the magnetic sensor of the present invention.
2. Description of the Related Art
As is well known, a magnetic sensor is principally used as a magnetic head of the HDD, i.e., a recording apparatus of a computer. Up to several years ago, the magnetic head for HDD had a sensing means, for a magnetic field, based on an induction current generated in a coil.
In recent years, however, the demand for a higher density and a higher speed has led to magnetic heads being provided with magnetic sensors capable of sensing a magnetic field by itself. The sensor is a magnetic sensor utilizing the magnetoresistive (MR) effect. Currently, there is a tendency to use a magnetic head utilizing the giant magnetoresistive (GMR) effect.
With the progress toward a higher recording density in the HDD as described above, the recording area per bit has been reduced and also the magnetic field generated has been reduced. In fact, the recording density of an HDD now available on the commercial market is about 10 to 20 Gbit/in2, and is increasing at a rate of doubling every year.
As it is necessary to respond to the above-described decreasing magnetic field range and to allow sensing of a very small change in the external magnetic field, at present, a magnetic head based on the spin valve GMR effect is widely used.
The magnetic sensor showing the spin valve GMR effect comprises a magnetic layer (pinned layer) with a fixed direction of magnetization and a magnetic layer (free layer) with a free direction of magnetization, and in the magnetic sensor, the electrical resistance can be changed by a variation in the angle between the directions of magnetization in these two magnetic layers. However, for this magnetic sensor, if a magnetic domain is contained in the free layer, it can generate Barkhausen noise, and therefore, to avoid the noise, the magnetic domain must be controlled. As a layer of a hard magnetic material (hard layer) is currently used as a magnetic domain control layer, an example of the magnetic sensor utilizing the spin valve GMR effect will be explained hereinafter with reference to FIGS. 1A and 1B.
FIG. 1A is a sectional view schematically showing a prior art magnetic sensor (SV-CIP element) utilizing the spin valve GMR effect, and FIG. 1B is an enlarged view of the dashed circle (section 1B) in FIG. 1A.
First, a lower magnetic shield layer 63 of a NiFe alloy or the like is formed, through a base layer 62 of Al2O3 or the like, on an Al2O3xe2x80x94TiC substrate 61 which is a body of a slider. A spin valve layer 65 is formed through a lower read gap layer 64 of Al2O3 or the like, and after patterning to a predetermined shape, a hard layer 66, made of a high coercive force layer of CoCrPt or the like, acting as a magnetic domain control layer, is formed on the two ends of the spin valve layer 65. Then, a conductive layer of W/Ti/Ta multilayer or the like is deposited to form a read electrode 67.
Next, an upper magnetic shield layer 69 of a NiFe alloy or the like is formed through an upper read gap layer 68 of Al2O3 or the like, thereby completing a basic configuration of a read head utilizing a spin valve element.
In this instance, the spin valve layer 65 is formed by depositing a base layer (underlayer) 70 of Ta having a thickness of 5 nm, a free layer 71 of NiFe having a thickness of 4 nm, a free layer 72 of CoFe having a thickness of 2.5 nm, an intermediate layer 73 of Cu having a thickness of 2.5 nm, a pinned layer 74 of CoFe having a thickness of 2.5 nm, a antiferromagnetic layer 75 of PdPtMn having a thickness of 25 nm and a cap layer 76 of Ta having a thickness of 5 nm, in this order, by a sputtering process while applying a magnetic field of 80 [Oe], for example.
For example, the composition of NiFe is Ni81Fe19, that of CoFe is Co90Fe10, and that of PdPtMn is Pd31Pt17Mn52.
The illustrated magnetic sensor is of CIP (current in plane) type, in which, as shown by arrows, a current is supplied in parallel to the surface of the spin valve layer 65, i.e. the surface of the magnetic sensor layer. As the hard layer 66 is arranged under the read electrode 67, its resistivity has no substantial effect on the characteristic (GMR characteristic) of the magnetic sensor.
In the formation of the read gap layer, the thinnest material capable of providing an insulation such as Al2O3 or SiO2 formed by CVD or the like is currently used. However, the minimum thickness of these materials is about 20 nm. Thus, in view of the fact that if the bit length becomes shorter, the thickness of the read gap layer cannot be reduced any further, the only possibility is to reduce the thickness of the magnetic sensor layer itself. However, apparently, the reduction in the thickness of the magnetic sensor layer is also restricted.
To avoid the above problems while satisfying the recording density of an HDD of not less than 80 Gbit/in2, it is necessarily considered to use a spin valve element (SV-CPP element) or TMR (tunnel magnetoresistive) element based on a CPP (current perpendicular to plane) system in which a current is supplied in the direction (at least the direction containing a perpendicular component) perpendicular to the surface of the magnetic sensor layer, because these elements do not require a read gap layer.
An example of the prior art read head of CPP type will be explained hereinafter with reference to FIG. 2.
FIG. 2 is a sectional view schematically showing the prior art SV-CPP element. As illustrated, a lower electrode 82 of NiFe capable of also acting as a lower magnetic shield layer and a spin valve layer 83 are formed on an Al2O3xe2x80x94TiC substrate 81. The spin valve layer 83 is etched to a predetermined pattern, followed by the lift-off process. In the lift-off process, a hard layer 84 of CoCrPt or the like and an insulating layer 85 of Al2O3 or the like are formed, on which an NiFe upper electrode 86 of NiFe capable of also acting as an upper magnetic shield layer is formed.
As described above, with the SV-CPP element, a read gap layer is not required. Further, as the upper and lower electrodes can also act as a magnetic shield layer, a whole thickness of the element can be reduced as compared with the SV-CIP element described above.
In this magnetic sensor of a CPP type, however, there is a problem that since the hard layer 84 is in direct contact with the spin valve layer 83, the sense current can escape as shown by arrows in FIG. 2 to the hard layer 84, thereby causing a reduction in the GMR characteristic.
To prevent the reduction in the GMR characteristic, the following methods are conceived:
Method 1:
As shown in FIG. 3, an insulating layer 87 is inserted between the hard layer 84 and the spin valve layer 83 so that the hard layer 84 may not be in direct contact with the spin valve layer 83.
Method 2:
As shown in FIG. 4, the hard layer 84 and the spin valve layer 83 are in direct contact with each other. The current supplied to the hard layer 84, however, is reduced by applying the specific arrangement (overlay structure) of the upper electrode 86 of NiFe.
Method 3:
As shown in FIG. 5, a magnetic insulating material such as a ferrite is used as the hard layer 88.
Among these three methods, the method 1 is not suitable because the spin valve layer 83 and the hard layer 84 are spaced from each other, and thus the controllability of the magnetic domain is reduced.
The method 3 suffers from the problem that since the magnetic characteristic (Br: residual magnetization) of the magnetic insulating material is small, it cannot be practically carried out.
Further, the method 3 suffers from the following problems:
First, the portion of the upper NiFe electrode 86 in contact with the spin valve layer 83 is at the center of the spin valve layer 83, and therefore is required to be smaller than the width of the spin valve layer 83. In view of the requirement of a positioning accuracy, it is difficult to easily produce the sensor with a high yield.
Secondly, depending on the layer structure such as the spin valve layer of the magnetic sensor, a low-resistance layer such as an Au antioxidation layer or the like is essentially disposed as the uppermost layer of the magnetic sensor layer, thereby posing the problem that the current from the upper electrode terminal can expand so widely as to escape to the hard layer.
It is difficult to solve all of these problems at the same time. To prevent the sense current from escaping to the hard layer, for example, a more complicated layer structure is required in the sensor.
The inventors of this application noted that the magnetic sensor (SV-CPP element) described above with reference to FIG. 1 has a simple structure, and it will become possible to provide a spin valve element of CPP type or TMR (tunnel magnetroresistive element) having a simple structure, along with satisfactory characteristics, if the current can be prevented from escaping into the hard layer of the element.
That is, the present invention is directed to reduce the reactive current as a result of an increase in the resistivity of a hard layer which acts as the magnetic domain control layer in a CCP-type magnetic sensor having a simple configuration.
One object of the present invention is to provide a magnetic sensor, particularly a spin valve element of a CPP type or a TMR (tunnel magnetoresistive) element having a simplified layer structure, along with a high GMR characteristic, without suffering from the problem such as an escape of the sense current to the hard layer, reduction in the controllability of the magnetic domain, low Br value (residual magnetization) and difficulty in positioning of the layers.
Another object of the present invention is to provide a magnetic sensor which is useful as a reproduction head or read head in a higher recording density magnetic recording apparatus such as a hard disk drive (HDD).
Still another object of the present invention is to provide a compact and high performance reproduction head using the magnetic sensor of the present invention.
In addition, another object of the present invention is to provide a compact magnetic recording apparatus satisfying a higher recording density and other requirements.
These objects and other objects of the present invention will be easily understood from the following description concerning the preferred embodiments of the present invention.
In one aspect thereof, the present invention resides in a magnetic sensor having such a structure that a hard layer for controlling the magnetic domain, formed of a conductive hard magnetic material, and a magnetic sensor layer are at least partially in direct contact with each other, and current flows in the direction wherein at least a main component of current is perpendicular to the surface of the magnetic sensor layer, in which the current flowing in the magnetic sensor layer and the hard layer is controlled by changing the resistivity of the hard layer.
In another aspect thereof, the present invention resides in a magnetic sensor having such a structure that a hard layer for controlling the magnetic domain, composed of a conductive hard magnetic material, and a magnetic sensor layer, are arranged at least partially in contact with each other, and current flows in the direction wherein at least a main component of current perpendicular to the surface of the magnetic sensor layer, in which the hard layer has a multilayer structure comprising a Co-based alloy and an insulating material of a non-solid solution.
Further, in another aspect thereof, the present invention resides in a magnetic head comprising a magnetic reproduction head (hereinafter, also referred to as xe2x80x9cread headxe2x80x9d) mounted therein, in which the reproduction head comprises the magnetic sensor of the present invention.
Furthermore, in still another aspect thereof, the present invention resides in a magnetic recording apparatus which comprises, at least, a magnetic head, a magnetic recording medium, a mechanism for rotating the magnetic recording medium, an arm member for mounting the magnetic head and a mechanism for moving the magnetic head as a function of moving the arm member, in which the magnetic head comprises the magnetic sensor of the present invention as a reproduction head.